feat(stock-pool): unify target execution, durable intent state and ETF rules

crates/fidc-core/src/instrument.rs

@@ -27,6 +27,12 @@ pub struct Instrument {
 }
 
 impl Instrument {
+    /// Classification from the admitted security master, never a code prefix
+    /// or a name substring. This does not grant T+0 settlement eligibility.
+    pub fn is_exchange_traded_fund(&self) -> bool {
+        matches!(self.board.trim().to_ascii_uppercase().as_str(), "ETF" | "EXCHANGE_TRADED_FUND")
+    }
+
     pub fn effective_round_lot(&self) -> u32 {
         self.round_lot.max(1)
     }